Device for supporting a horizontal guided glass strand

ABSTRACT

The invention concerns a device for supporting a horizontal guided, continuous glass strand;  
     with a number of supporting blocks, which each exhibits a supporting area, facing the glass strand;  
     the individual supporting block in the area of the supporting area is made from a porous, gas-impermeable diaphragm body;  
     the diaphragm body is connected to a source of compressed gas for conveying gas through the supporting area.

[0001] The invention concerns a device for supporting a horizontalguided, continuous glass strand.

[0002] The Danner-Technique and the Vello-Technique are used for theindustrial production of glass rods and glass tubes up to diameters ofapproximately 100 mm. With the Danner-Technique the glass flows from anozzle on top of a rotating tilted pipe, through which, in the case ofproducing tubes, a glass is blown and a glass strand is pulled offcontinuously from the tip. With the Vello-Technique a ring nozzle,through whose center the glass is blown for the tubing production,creates the glass strand.

[0003] Tube drawing techniques have become known for example from DE 10054 804 A1.

[0004] With the usual techniques for the production of glass rods orglass tubes, the hot and ductile glass strand is directed into thehorizontal level, cooled down over the length of the drawing bench andfinally separated into sections of the desired length. The glass strand,which is still hot, is supported along the drawing path. This takesplace usually by means of rollers or supports from a material, whichleaves fewest possible traces on the surface of the glass strand.

[0005] Wood and graphite are the materials usually used for theserollers. V-shaped blocks made from the same materials are used insteadof the rollers if extremely quiet running of the glass strand isdemanded within the drawing path; the recess of the V-shaped blocksguides the glass strand.

[0006] The good lateral guide properties are achieved while acceptingthe facts that the strand slides on the support and that there is thedanger of developing scratches.

[0007] The small supporting surface, which the rollers offer to theglass strand, causes the glass strand (especially in its hot area) to bedeformed during transport over the rollers, which in return causes animpairment of its dimensional accuracy and especially problems withovalness. Furthermore, heat is removed from the glass strand along thecontact line to the rollers. The nonuniform heat distribution over thecircumference of the glass strand leads with further cooling todistortion and bending of the glass strand. In addition, the contact tothe rollers transfers dust and dirt on the glass strand.

[0008] The guide rollers and guide blocks are especially in the hot areasubjected to distinct wear by abrasion. This abrasion creates for hispart contaminations on the glass strand surface. During the progressivewear the occurrence of the scratches created by the supporting deviceincreases, until the rollers and blocks must be exchanged after sometime.

[0009] DE 31 25 521 A1 describes a device for conveying and supporting ahot, continuous glass tube. The supporting device exhibits a V-shapedrecess, which forms a supporting area for the glass tube. The supportingarea exhibits drilled holes in the vertex of the V, which are connectedto compressed air. Compressed air is to take the glass tube off from thesupporting area. However, in the range of the legs of the V-shapedsupporting area approximation of the glass tube to the walls of the legstakes place and therefore also contact.

[0010] This leads to a mutual impairment. On the one hand scratches candevelop on the exterior of the glass tube, on the other hand materialwear of the supporting device takes place, especially if a soft materialsuch as graphite is used for it.

[0011] A design variation is know as state of the art, in which theglass tube strand is guided between two walls bent against each other,which are usually out of sheet metal, and is carried on air, whichdischarges from the gap between the walls. Usually these devices arepresent only in first few meters; rollers do the further transport ofthe glass strand. In such devices one tries to stabilize the glassstrand centered on a gas cushion by means of suitably guiding the gasthat is emerging from a gap under the glass strand. However, lateralcontact of the glass strand with the walls cannot always be prevented,so that in these cases the surface of the glass strand is damaged orcontaminated.

[0012] A freely floating guide of the freshly formed glass strand oncompressed air nozzles would be possible. In this case no contact canoccur between glass strand and firm materials. However, the necessaryairflow for supporting the glass strand would be so large, that thenozzles would cause an inadmissibly high noise level. Furthermore thereis the risk that the gases impacting the glass strand surface with highspeeds deform the glass strand especially in its hot area. Besides, thisprinciple is not economical due to the high costs of compressed air.

[0013] The invention is based on the task to design a device of theinitially described kind in such a manner that a glass strand—solid orhollow—originating from a continuous casting unit, is horizontal guidedand supported, without having contact with the firm environment, so thata damage of the glass strand and/or wear of the supporting blocks areomitted, with good dimensional accuracy of the glass strand as well aswith low capital investment cost and low operating cost.

[0014] The features of the individual claims solve this task.

[0015] The device according to invention thus creates a gas cushion forthe support of the glass strand. The gas cushion is created thereby bythe means of a fine-porous, gas-permeable diaphragm body, from which gasemerges in finest distribution. This way a gas cushion can be formed,which can be created on the one hand with gas throughput, and whichimpinges on the blown on areas of the glass strand as symmetrical aspossible.

[0016] Thus the difficulties connected with rollers or firm supports,like the local extraction of heat at support points and the risk ofdeformation, are eliminated. Contrary to the rollers or firm supportsthe carrying force will transfer over a substantially larger area to thetubing strand, which prevents the risk of deformation. Moreover, theheat dissipation from the glass strand is homogenized, since no localcontact between the glass strand and the supporting device takes place.The heat dissipated by the supporting gas is removed from the glassstrand over a large surface area.

[0017] An interesting thought of the invention consists of providing thediaphragm bodies with channels for passing the compressed gas and tolocate the channels in a certain distance to the gas emergingarea—called from now on “supporting area”—, generally parallel to thesupporting area. Thereby it is possible to use diaphragm bodies madefrom a material with relatively low strength and to design the diaphragmbodies relatively thick-walled, so that on the one hand there is no riskof fracture, and that however on the other hand the compressed gas hasto cover only a short distance from the channel to the supporting area,so that the pressure of the compressed gas can be relatively low.

[0018] The invention is described in more detail with the help of thedrawing. The following is shown individually:

[0019]FIG. 1 shows schematically a continuous casting unit of the Velloprinciple.

[0020]FIG. 2 shows a supporting block for a continuous casting unit in asection perpendicular to the glass strand axis.

[0021]FIG. 3 shows a second design variation of a supporting block.

[0022] The device represented in FIG. 1 exhibits a feeding head 1. Atthe base of the feeding head 1 sits a discharge ring 2. Centered in thisring is the tube-drawing needle 3. The needle consists of a long shank3.1, whose lower end is extended downwards conically. This cone, thepinhead 3.2, is scarcely below the discharge ring. The needle shank ishollow for guiding the gas atmosphere 7 (drilled hole 3.4), so that thegas atmosphere can be blown through. The needle can be traversed inhorizontal and vertical direction.

[0023] The molten glass mass 4 flows through the annular gap betweenneedle 3 and ring 2 and expands over the conical pinhead 3.2. From theedge of the pinhead, the tear-off edge 3.3, it flows downwards and formsinto a bulb. The in such a way created hollow strand 5 is bent in thehorizontal direction before solidifying while hanging freely and pulledoff over supporting blocks 10 according to the invention with a drawingmachine.

[0024] The gas pressure of the gas atmosphere 7 can be regulated, sothat in connection with different drawing rates of the glass amount tobe processed a broad dimensional spectrum can be manufactured.

[0025] The supporting block 10 represented more accurately in FIG. 2carries the glass strand 5. The supporting block 10 is built as follows:one recognizes two diaphragm bodies 10.1, 10.2. These consist of afine-porous material, for example of carbon materials. They are builtcompletely identical and symmetrically arranged in such a manner thatthey form a V with one another. The supporting block 10 can be builtasymmetrically as well.

[0026] Furthermore a pressure housing 10.3 is intended. It exhibits twoinlets 10.4, 10.5 for compressed gas. Between the inlets 10.4, 10.5 is afurther gas inlet 10.6, which can be used for passing in gas of relativelow excess pressure.

[0027] The compressed gas passed into the inlets 10.4 and 10.5 passesthrough the pores of the diaphragm bodies 10. 1, 10.2 and arrives at thesupporting areas 10. 1. 1, 10.2.1 of the diaphragm bodies 10.1, 10.2,where it emerges. It forms a gas cushion, on which the glass strand 5 soto speak swims.

[0028] It is necessary in each case that the material of the diaphragmbodies 10.1, 10.2 is an open-porous material, so that gas from theinterior of the pressure housing 10.3 can pass through to the supportingareas 10.1.1 and 10.2.1. An open-porous carbon material is preferred. Itexhibits very good emergency running properties in case of the failureof the gas supply and also leaves no disturbing traces on the glassstrand surface with brief contact. Beside carbon also open-porous sintermetals or metal fabrics are applicable for these parts of the device.They are used preferably in applications, in which with carbon nosufficient long time creep strength can be achieved with hightemperatures.

[0029] In temperature ranges over 900° C., where even regular metals arepushed to their load limits, the use of porous ceramics such as SiC orCordient or of porous precious metals is possible.

[0030] The angle α that the two diaphragm bodies 10.1, 10.2 form withone another, depends on the outside diameter of the glass strand 5. Thearrangement can be done in such a manner that the angle α is adjustable.For glass strands with large diameter flatter angles are favorable, forthin glass strands pointed angles. Some combinations of strand diameterand angle can be taken from the following table:

[0031] Interrelationship between glass strand diameters and supportangles Glass strand diameter Angles  3 mm  90° 12 mm 110° 30 mm 135°

[0032] Inlet 10.6 for gas with low excess pressure is designed in such amanner that the gas flow divides and strokes preferably along thesupporting areas 10.1.1 and 10.2.1. This division of the gas flow cantake place by means of bent drilled holes, recesses misaligned againsteach other, recesses or other things built in the gap.

[0033] Air is the first choice for gas. In addition, other gases can beused. Gas can exercise besides its supporting function a temperatureequalization function, thus that it exhibits a certain temperature.

[0034] The whole device is preferably separated into individualsegments. These can be arranged directly one behind another to permit aconstant support of the glass strand especially in its hot area. Withincreasing cooling of the glass strand however it becomes moremechanically stable, so that the segments with increasing distance ofthe hot area can be arranged in larger distance. Thus the operating costcan be reduced compared to a continuous device.

[0035]FIG. 3 shows again two diaphragm bodies 10.1, 10.2 with its twosupporting areas 10.1.1, 10.2.1. The special feature of these diaphragmbodies are channels 10.1.3, 10.2.3. The channels run parallel to thesupporting areas 10.1.1, 10.2.1. Several such channels 10.1.3, 10.2.3are arranged behind each other—in direction of the glass strand axis.

[0036] The reason for this design variation is the following:

[0037] A very brittle material with comparatively low strength can beused as diaphragm material, because the diaphragm bodies can be madevery thick, so that the strength is acceptable. Nevertheless is thedistance, which the compressed gas must cover through the diaphragmmaterial until it arrives at the supporting areas, relatively short. Thechannels 10.1.3, 10.2.3 can be located relatively close to thesupporting areas 10.1.1, 10.21.

[0038] As an alternative to the design variation in accordance with FIG.3 it could be considered to create the two diaphragm bodies 10.1, 10.2very thin and to put them on top of a rigid base. However, this designvariation could be expensive and complicated.

1. Device for supporting a horizontal guided, continuous glass strand(5); 1.1 With a number of supporting blocks (10), which each exhibitsone supporting area (10.1.1, 10.2.1), facing the glass strand; 1.2 Theindividual supporting block (10) is in the area of the supporting area(10.1. 1, 10.2.1) made from a porous, gas-permeable diaphragm body(10.1. 10.2); 1.3 The diaphragm body is connected to a source ofcompressed gas for conveying gas through the supporting area (10.1.1,10.2.1).
 2. Device according to claim 1, characterized by the fact thatan additional gas connection (10.6) is intended for passing compressedgas against the bottom of the glass strand (5).
 3. Device according toclaim 1 or 2, characterized by the fact that the diaphragm body (10.1,10.2) consists of open-porous carbon material.
 4. Device according toclaim 1 or 2, characterized by the fact that the diaphragm body (10.1,10.2) consists of open-porous ceramic material.
 5. Device according toclaim 1 or 2, characterized by the fact that the diaphragm body (10.1,10.2) consists of open-porous sinter metal.
 6. Device according to oneof the requirements 1 to 5, characterized by the fact that the glassstrand (5) is created by a continuous casting unit.
 7. Device accordingto one of the requirements 1 to 6, characterized by the followingfeatures: 7.1 The individual diaphragm body (10.1, 10.2) exhibitschannels (10.1.3, 10.2.3) for passing compressed gas; 7.2 The channels(10.1.3, 10.2.3) are in the material of the diaphragm body (10.1, 10.2)in a distance to the supporting area (10.1.1, 10.2.1).
 8. Deviceaccording to one of the requirements 1 to 7, characterized by the factthat two diaphragm bodies (10.1, 10.2) are intended, which are arrangedV-shaped—in a section perpendicular to the glass strand axis.
 9. Deviceaccording to claim 8, characterized by the fact that the additional gasconnection (10.6) is intended for passing a compressed gas against thebottom of the glass strand (5) in the apex of the V.